A thickness measuring system for measuring a thickness of a planar plate-shaped member on a conveyer belt includes a processor, a first distance measurer and a second distance measurer. The first distance measurer on one side of the conveyor belt can emit and receive a first light beam parallel to the conveyer belt for reflection off the planar plate-shaped member, and calculate a first distance between the first distance measurer and the plate-shaped member. The second distance measurer on the other side of the conveyor belt can emit and receive a second light beam and a third light beam for reflection off the planar plate-shaped member, and calculate a second distance between the first distance measurer and the plate-shaped member and a third distance between the second distance measurer and the plate-shaped member.